Synchronized oscillator circuit



April zo, 194s.

w. E.- BRADLEY A 2,440,073

SYNCHRONIZED` OSCILLATOR CIRCUIT Filed Oct. 9, 1945 2 Sheets-Sheet 1 April 20, 1948. w; E. BRADLEY S'YN'HRONIZED OSCILLATOR CIRCUIT Filed Oct. 9, 1945 2 Sheets-Sheet 2 /q. 4.

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nl IIIIIIIIHNUHHIINH .HUNIIIIIIIIHHH Patented pr. 20, 1948 UNITED STATES PATENT CFFICE Y SYNCHRONIZED OSCILLATOR CIRCUIT William E. Bradley, Swarthmore, Pa., assignor, by mesne assignments, to Philco Corporation,

Philadelphia, Pa., a corporation of Pennsylvania j the source of frequency-modulated signal,

Application October 9, 1945, Serial No. .621,343

11 Claims. (Cl. Z50-36) This invention relates Ytofrequency modula-f` tector of the synchronized oscillator type which` is characterized in that it does not absorb powerl from the source of frequency-modulated signal, and it is insensitive'to amplitude variationsand therefore does not require' the use .of a limiter.

in thedetector system of the said co-pending application, the oscillator is synchronized with the frequency-modulated carrier signal by a radio frequency control vol-tage which is in quadrature relationto the oscillator signal.

The present invention relates to a system which closed in the said co-pending application, but which diifers specifically from that system in respect to the manner in which the quadrature control signal is derived. Like the system of the said,

`20 y embodies the broad principles of the system dis"` co-pending application, the system provided by` the present invention does not absorb power from and is insensitive to amplitude modulation.

The principal object of the presen-t invention,

therefore, is to provide a novel frequency modu-- lation-responsive .circuit which is insensitive t amplitude modulation.

Another object of the invention is to provide a circuit which is capable of transmitting frequency modulation with substantial power gain.

A further object of the invention is to provide an improved frequency modulation detection system comprising a novel frequency modulation amplifier circuit and a frequency modulation detectorby means of which combination the fre" quency-modulated signal is efficiently detected without response toamplitude modulation and without employing any amplitude limiter.

Still another object of the invention is to provide a novel frequency modulation-responsive circuit of the synchronized oscillator type in which theoscillator is synchronized by means of a quadrature signal derived by uniqueoperation of a synchronizing tube, as described hereinafter.

2 Other objects and features of the invention will be apparent from the following detailed description in connection with the accompanying drawings, in which Figs. 1 to 3 are schematic illustrations Aof different embodiments of the invention; and

Fig. 4 comprises a series of explanatory diagrams.

Referring first to Fig. l, there is illustrated one form `of a frequency modulation detection system embodying the present invention. The system comprises essentially a vacuum tube I, an oscillator 2, certain connections hereinafter described by which the tube I is adapted to synchronize the oscillator with a frequency-modulated signal, and a frequency modulation detector 3 connected to the oscillator so as to receive a frequency-modulated signal therefrom. w Since the purpose of tube I is to synchronizelthe oscillator 2 with the incoming frequency-modulated signal, tube I may be aptly designated the synchronizing tube, and it willbe thus referred to in the description. The synchronization of` i the oscillator 2 is accomplished, according to the present invention, by a unique class C operation of the tube I, which will be described later with specific reference to the explanatory diagrams of Fig. 4. i

"Ihe synchronizing tube I is a multi-grid tube having RF input grids 4 and '5, and an output electrode or anode 6. The tube is adapted to receive a frequency-modulated signal by way of the coupling condenser 'I andthe grid resistor 8. Ii desired, acathode resistor 9 and shunt condenser I0 may be employed as a biasing means for the control grid- 4. Y

The oscillator 2', as shown in Fig. 1, may comprise a tuned plate oscillator circuit operating in the usual class C manner. Such circuit may comprise a tube I l, a resonantV tank circuit I2 including shunt-connected inductance and capacitance elements I3 and I4, and an inductive feedback circuit I5 vincluding coil I6, condenser Il and resistor I8; The necessary'plate Voltage for tube IImay beV supplied by the connection I9 to the mid-point of the inductance coil or winding I3.

The anode or plate -6 of the synchronizing tube I is connected to the upper endof the tank circuit I2 through=condenser 20. The necessary plate 3 of the D. C. plate voltage is such as to effect a de'- sired operation of the tube I as will be described further hereinafter. The grid 5 of tube I is connected to the lower end of the tank circuit I2 through the condenser 22, and this grid is also supplied with a bias Voltage by way of resistor 23. The specic value of the bias voltage applied to grid 5 is also important in that it helps to effect the desired operation of tube I, as will be seen later.

The frequency modulation detector 13.; may be oi conventon`alform ahd therefore', it y,isnrl'eprevsented simply in block form. For example, the detector may be of the well known Seeley type, and may be coupled in any suitablemanner tothe plate circuit of the oscillator tub'el I. The audio output from the detector is derived by way of the output connection 24.

The operation of the scribed with the aid of the explanatory diagrams of Fig. 4. In Fig. Ma) thereis represente,d the alternating Voltage e0 generat'dby theos'cillator 2, while in Fig. LMe) there is represented theunmodulated carrier signal es which is supplied to the grid s si the swnsiiisniznsiube- L It should be. nstss with@ .If uhsllrslsrisr f fhsfsssillabor, voltage lt susststetiellr se" .s1 to thefrequency of the carrier signal e'sQbu the 'oscillator voltage isy in phasekoppositionto the 'carrier signal, i-e1890uts-fphassthsr Wit/hf. d ,l

The oscillator voltagedisappliedltothe p te of tube I througlil the condenser. Theil), C. Plats v sltage swelled. to, the plate s, frrlfthe source Eels, sllqh that@ t respect tosathsds) arrrslm 60% of eachcycleuas hir n,Fig.l(b) wherein the plate voltageempi l A similarvsltaeeff frornthe lowe appliedjtth ends@ issuer bris ister-v vals, twice @urinasash 5:61a @ssh wel in the f actthstit maketh@ operaties@ the,...

systern'substantiayy; insensible tochanges vin plats- Current-wavieshapes..

When the frequencyfmodulated.signalisab its senterirequency. .the'plate current. nl lsss is "are of substantielle equa1.emp1itude-..;A?.silh the plate current contains no frequency `comspines-Hinter about onsteeth Pf;alsyslskiilrapsn ,QQ sans plate current ing signal, siibst'a'ntially'aslesrileclv in the aboveidentified copending application.

Suppose, for example, that the frequency of thev incoming 4farrier signal es increases, which is equivalent .to a `phase shift slightly to the left in Fi 4('3' r`I Tc'ase, the odd-numbered plate Ycurrent flig, 4(1d) occur during portions of the positivegalternations of the signal Voltage e s, whi le the evennumbered plate current pulses occur on-lyduring portions of the negative alter- Viiagt'ionsu of the signal Voltage es. This means that throughout the interval of each odd-numbered plate current, pulse thensignal voltageY es aids the n'tgwhil throughoutthenterd lse the ignal'voltw ,f T'lgjrrent. Conetlyfd nuns.; di tenerti-pulsera@ 30 lincreased m'agr'iitude'inproporticjnA te the' frequency deviation of UAthe `signal, while '"jtlije leven- Flein( one or the other of the quadrature signals predorninates and Varies the frequency of the oscillator. 1

tive to amplitude modulation.l .Any amplitude modulation of the incoming signal willnot produce, nor aect,A the control action above described, and will not affect the oscillator. Thus it will be seen that the system discriminates againstany amplitude variation or modulation of the incoming signal, without theaid of `a limiter.V n I Furthermore, the system does not absorb power from the source of frequencyjmodulated signal, and only a small input signal is'required. The quadrature signal for synchronizing the oscillator is produced entirely by the synchronizing tube circuit under control of the input signal voltage. Moreover, it should be noted that the current pulses delivered from the synchronizing tubeV to the oscillator tank circuit do not. affect the energy in the tank circuit, since thepulses are delivered thereto when the tank voltage is midway between its maximum and minimum values, i. e. when the tank voltage is passing through its zero value.

By reason of its novel'features, the-system is adapted to discriminate completely against ainplitude modulation and to transmit frequency modulation with substantial power gain. The frequency-modulated signal is readily detected by a conventional frequency modulationdetector as represented by the block 3.

In Fig. 2, there is shown arnodied form of the system in which the oscillator 2 is of a different type than that employed in Fig. 1. In this instance, the tank circuit `I2 is connected in the grid circuit of the oscillator tubeA II, and-issupplied with feedback voltage by way of the coil 25 connected in the cathode circuit. Plate voltage for the synchronizing tube I is supplied b-y way of the connection 26 to the midpoint of the tank coil I3. It will be noted further that the grid 5 of tube I is connected to ground, the bias therefore being derived in part by means of the resistor-condenser combination 9--I IJ, and in part by means of the grid condenser-grid leak combination 22-23.

Except for the specific differences noted, the system of Fig. 2 is similar to that of Fig. l, and the corresponding elements in Fig. 2 are simi* larly designated. The system of Fig. 2 operates in the same manner as does that of Fig. 1, as hereinbefore described.

In Fig. 3, there is illustrated a further modification of the system in which the synchronizing tube I has two grids 5a and 5b in place of the grid 5 of the preceding figures. The two grids 5a and 5b are coupled to the opposite ends of the tank circuit I2 through condensers 22 and 2l respectively. The oscillator 2 is similar to that of Fig. 2.

In the operation of the system of Fig. 3, the grids 5a. and 5b control the production of the plate current pulses. Thus the voltages applied to the grids 5a and 5b control the plate current pulses in the same way that the voltages ep and eg in Fig. 4 perform this function. Except for the brief pulse intervals, the voltage on one or the other of the grids 5a and 5b is below the plate current cut-olf value, thus preventing plate current from flowing during most of each cycle. The two grids should of course be properly biased to obtain the desired control action. The bias for these grids may be obtained from the resistor- As previously indicated, the system is insensi- .condenser combination 9-I0, or it may be obd vtainedvfrom an additional bias source.

Although the invention has been described with particular reference to the several embodiments illustrated, it willbe4 apparent that it isrcapable .of other forms of physical expression, and is not `to be limited by the disclosure herein,' but only bythe scope of the appended claims.

I claim: Y

l. In a frequency modulation-responsive circuit, a vacuum tube adapted to receive an vincoming frequency-modulated signal, an` oscillator adapted to generate an alternating voltage whose normal frequency is substantially equal to the frequency of theunmodulated signal, means for operating said tube so as to produce current pulses substantially centered about the zerovoltage `points of vthe unmodulated signal, there `being two pulses for eachV cycle of said signal, and

. 3. In a frequency modulation-responsive circuit, a vacuum tube adapted to receive a frequency-modulated signal, an oscillator including a `resonant tank circuit, means for controlling said tube Vso as to produce two current pulses during each cycle ofthe oscillator voltage, said pulses having their relative amplitudes varied by the frequency variations of said signal, and means for applying said pulses to said tank circuit to control the frequency of said oscillator.

4. In a frequency modulation-responsive circuit, a vacuum tube including a plate, a control grid, and at least one other grid, an oscillator,.

means for deriving opposite-phase voltages from said oscillator and for applying said voltages to said plate and said other grid respectively, means for causing said voltages to produce pulses of plate current in said tube, and means for applying to said control grid a frequency-modulated signal whose frequency variations produce variations of said pulses which vary the frequency of said oscillator accordingly. 5. In combination, an oscillator whose frequency is to be varied according to frequency variations of a frequency-modulated signal, a vacuum tube including a cathode, an anode and a plurality of control elements, means for supplying the vfrequency-modulated signal to one of said control elements, means connecting said anode and another of said control elements to said oscillator so as to apply opposite-phase voltages to said anode and said other control elements, and means for causing said voltages to produce pulses of plate current in said tube whose relative amplitudes are affected by frequency variations of said signal.

6. In a frequency modulation-responsive circuit, a vacuum tube including a control grid andV at least two other grids, an oscillator, means for deriving opposite-phase voltages from said oscillator and for `applying said voltages to said other grids, means for causing said voltages to produce pulses of plate current in said tube, and means for applying to said control grid a frequency- 7 inoclulatedsignai whos'elfrequencfrvariaicns psw ducel variations of saiipulises which vary/thefrequencyA of-said' oscillator'accordinelm 7'. En `a frequency :modulation-responsivesysgquadrature; control 'siginals comprising alternate- 1y occurringy pulses; which 'are -normallyfof the same magnitude, one oisaid l'signals tending lto raise the [frequency of said oscillator and'iil'ie-fother signal, ytending 'to lower the frequency `ef -thewosl cill'ator, and mea-ns Vforrelatively varying'llthe magnitudes of'said ysigna-ls` in response itc a frequency-modulated signal, `whereby'tcvarytrie-csfcillaitor frequency according yto the frequency Variations of said 'modillatedsignal.

A8. In a; frequency modulation-responsive system, an oscillator including a; resonant 'taule cirrcuit, mea-ns for, producing a pair of*'quaxlrature control* signals comprisingalternately loccurring pulses` which are normally off the same mag*- ni-tude; means for-applying said Vsignakls toA said tank; circuit, whereby one of che-signals tends to raise the frequexrcy"of` said-oscillator and the other signalr tends to 1ower-the frequencyo' the oscillator, and' means forrelative1y varyingfthe magnitudes vof s'aitigsignalsn in responsevtol'a'frire quency-rnorlulateclsignal', whereby' tofvary themslciliator frequency accordiifxg to #he frequency variations of saidmodul'ated signal;

9. In a frequency"moduiationeresponsive'sys'- tem,v an oscillator adapted to'produce-an alternatingvoltage ofpredeterminedfrequency; means for producingapar` off control;signalsccmprising alternately occurring pulsesrin coincidencwwith the zero-voltage points of-said voltage; said-pulses being normally,V of. thesame magnitude; means forv 'relatively varying: the magnitudes of"v -tli'e pulsesoconstituting,therespective control signals l.-espoase ma. nequenewmcdxuatedsignal, .and 'means for' utili-2mg saldi control signals te vanfy frequency vcoxuiesporiding tofftherequency of the nnmolduiatedcavrrier wave, producingtwo: current pulses during -eacl'r cyclefof theV umn@dul'atedi car- -erewavefan the oscillator voltage,v varying' the Vrelative amplitudes vci? said pulses according to frequency variations of the modulated carrier wave, and; varyinglthe operating frequency ofthe oscillator according' tof the lanIp'litucie variations ll. -I'n a system wherein Ait" is` desired to-synchronize an: oscillator' with a 'frequencysmoduh lated) carier- Wave; an oscillator whose' normal frequencyfcorrespondsto: tliaitdtle unmo'dxlated carrier Wave; means forproducing twocurrent pulses -deringeachcy'cieofftheunmoduiated carrier'waveandtlref oszxillatcrvoltage; and'for'causingetlr -relat'i'ven airxplt'udes"4 of said pulses" to" vary accordingV to yifi-'equemcy variations cfY the modulated" carrier wave, andfmeansffor utilizing said pulses to control* theos'cil-l'ator 'frequency according tothe frequency' varations'off the modulated cariierwave: 4

The following references` 'are' of record in" the Numbexj yName Date medew @charts-f June-16, 1942 2`3192-8J "-Roerts# Aug: T4; 1945 

